Sensors and controls are routinely deployed in plants and facilities to detect and control process conditions, equipment conditions, and environmental conditions. Many of these sensors/controls will be electrically tied to a master control panel or control area for monitoring/control of the sensors at a common location remote from the sensor. At the master control panel, actions can be undertaken to change a sensor/control state or configuration, log sensor/control data, or simply monitor the sensor/control for use in controlling the facilities' performance. Generally, the master control panel is located behind an IS barrier (in the safe area), as sensors/controls can be located in hazardous environments. Prior art measurement and control systems for use in hazardous locations consist of single, high-function devices which are responsible for gathering all of the data through a fixed number of dedicated inputs and implementing all of the control functions through a fixed number of dedicated outputs. All of the collection, computation and control must fall within the predefined capabilities of these devices. Consequently, these prior systems either contain more capabilities than required, are designed to meet only the required capabilities, or do not contain sufficient capabilities to meet the data measurement and archiving requirements. These single devices offer limited expansion capability and must be replaced with another device having greater capabilities if the system's application requirements are increased. Intrinsic safety concerns with a single high-function device increase with every input or output connected to the device. In order to maintain safe operating conditions in a hazardous area, the overall system needs to be carefully designed for intrinsic safety and the installer/system designer must exercise great care to ensure that intrinsic safety is not violated. These restrictive safety requirements limit the capacity of batteries placed in the hazardous location. The power requirements of these higher-function devices and the need for safety components also prevent miniaturization of these systems.
Some facilities have provided for communication between sensors to allow data from sensors/controls to be shared, such as in a master/slave relationship. However, use of networked devices behind an IS barrier provides severe power restrictions on downstream devices due to the nature of an IS barrier, and hence limits the ability to install devices on a network with a common power bus. Even with networked sensors, control of downstream networked devices generally resides in a remote sensor monitoring site, where data is stored and archived. As real time communication is ongoing between the sensor/control devices and the remote monitoring site, it is difficult to control power consumption. Further, when additional sensor/control devices are added to an existing configuration where data is to be shared between devices, existing devices must be manually modified to share and use the new device's data. This requires user intervention and is a cumbersome and time consuming process.
It is desirable to have a distributed sensor/control device network where local data is stored and transmitted upstream upon request of an upstream device. It is desirable to have low power consumption devices, with battery backup shared between devices to allow for continued operation when the supplied power feed is interrupted; it is desirable to have sensor/control devices with the ability to communicate characteristics between devices, including communication parameters, to allow devices to detect new devices placed on the network, determine device characteristics, and allow for integration of the new device into the network by allowing upstream devices to set configuration parameters to downstream devices.